Continuous casting is a known process for casting various metals including both ferrous and non-ferrous metals into billets. In a conventional casting process, molten metal is tapped from a furnace into a ladle having a nozzle in its bottom wall. The nozzle can be opened and closed by various devices such as a stopper or sliding gate.
The molten metal is poured through the nozzle of the ladle into a tundish. The tundish also has a nozzle in its bottom wall, and molten metal is poured through the tundish nozzle into a mold. One purpose for the tundish is to control the flow rate of the metal into the mold.
The mold is generally water cooled, and the metal poured therein forms a strand or billet. A peripheral region of the molten metal solidifies to form a skin which surrounds the molten interior of the billet. As the billet is pulled through the mold, it is cooled further and the skin progressively thickens.
Before removal of the billet from the mold can be started, the skin must be sufficiently thick to support the molten metal within the billet. More specifically, the skin must be sufficiently strong to withstand the head of metal within the billet when it is removed from the support of the mold. If the skin is too thin, the molten metal breaks out through the skin. If the breakout is large, it becomes necessary to abort the cast.
An obvious partial solution to the breakout problem is to increase the rate of cooling of the billet thereby increasing the rate at which the skin thickens. Unfortunately, the billet cannot be cooled at a maximum rate because its properties deteriorate if this is done. Alternatively, the rate of billet movement, i.e., the speed of the casting operation could be reduced, and/or the length of the mold increased. However, neither of these are commercially desirable because each results in increased cost.
During a casting operation the billet is typically moved and guided by a series of rolls. The fluid pressure within the billet caused by the head of metal causes the skin to bulge between adjacent rolls. These bulges increase the power requirements to move the billet.